The findings, presented in Copenhagen at the annual congress of the European League Against Rheumatism, may help identify patients with rheumatoid arthritis needing more intensive early therapy.
Study leader Dr. Gael Mouterde of Lapeyronie Hospital in Montpellier, France, said patients whose first symptoms occur in winter had greater erosion and joint space narrowing and their symptoms were rated more severe at six months than those patients whose symptoms appeared in summer.
Similarly, patients' symptoms after six months were worse if their first symptoms had occurred in winter versus autumn. This effect was not observed at a 12-month follow up. The researchers suggest initial environmental factors probably exert less of an long-term effect.
"During our study of predictors of radiographic progression, we have unveiled a distinct relationship between rheumatoid arthritis progression and seasonal onset and postulate that this could be as a result of either a vitamin D deficiency or environmental factors, such as winter viruses, influencing protein citrullination," Mouterde said in a statement.
Anti-citrullinated protein antibodies, Mouterde said, are often found in the immune systems of rheumatoid arthritis patients and may assist in identifying patients at a higher risk of developing structural damage.